This invention relates generally to dither motors, for example, dither motors incorporated within ring laser gyroscopes.
In a ring laser gyroscope, two electromagnetic waves in the form of monochromatic light beams are produced which are propagating in opposite directions. A rotation of the ring laser gyroscope about its input axis increases the path length for one light beam whereas the path length for the other light beam is reduced. The resulting path length change produces a frequency shift within each of the light beams since the oscillating frequency of the laser beams depends on the length of the laser path. Therefore the frequency difference is a function of the rotation rate.
At low rotational rates the frequency difference between both light beams becomes small and both light beams have the tendency to oscillate on the same frequency which is sometimes referred to as lock-in. In order to prevent this mutual interference of both light beams at low rotational rates it is well known to impart a rotary oscillation to the ring laser gyroscope so that the known lock-in effect is eliminated to a large extent.
In order to produce the rotary back and forth oscillation normally a mechanical oscillating device is provided which imparts a dither motion to the ring laser gyroscope. Such a device is commonly referred to as a dither motor and includes a spoked wheel (dither spring). In one known configuration, supports extending from a hub of the dither motor engage a bore formed in each ring laser gyroscope laser block. In another configuration the entire dither motor is placed within the bore of the laser block.
Piezoelectric transducers that are mounted on the spokes of the dither spring produce an oscillating back and forth (dither) movement of the ring laser gyroscope when they are driven by appropriate signals. Such transducers are referred to as drive transducers. Other piezoelectric transducers that output a signal based on the dither movement are referred to as pickoff transducers and are utilized as a feedback device in controlling the oscillation of the dither motor.
Dither motors that are incorporated within ring laser gyroscopes typically include both drive and pickoff piezoelectric transducers. One known dither motors incorporates pickoff piezoelectric transducers that are separate from the drive piezoelectric transducers. These pickoff piezoelectric transducers have a different size and are placed in a separate location than the drive piezoelectric transducers. The separate pickoff and drive piezoelectric transducers add stiffness to the dither spring and cost to the ring laser gyroscope product. In addition, pickoff piezoelectric transducers in a location separate from the drive piezoelectric transducer have a higher variation in phase relative to drive and pickoff voltages generated.